The adoption of the brake override systems (BOS) in which a brake is given priority at the time of simultaneous operation of an accelerator pedal and a brake pedal as seen in Patent Document 1 for example, in vehicles has made recent advancements. The BOS gives priority to the brake at the time of simultaneous operation of the accelerator and the brake by making a required accelerator operation amount used for controlling a drive force of the vehicle (for example, controlling a throttle opening degree of the engine) smaller than an actual accelerator operation amount, that is, an actual pressing amount of the accelerator pedal and by making the drive force of the vehicle smaller than a value that corresponds to the actual accelerator operation amount.